1. Field of the Invention
The present invention relates to a display device and a method for producing the same. In particular, the present invention relates to a display device which involves no fear of any incomplete light off state, and a method for producing the same.
2. Description of the Related Art
FIG. 38 shows an example of a large screen display in which a plurality of display devices are arranged on an optical waveguide plate. The large screen display 100 has, for example, such features that it is of the direct vision type, it is of the thin type, it has a high luminance, and it has a wide angle of visibility. A plurality of display devices 10 as described later on are arranged in the vertical direction and in the lateral direction respectively on a first surface (back surface) of the large optical waveguide plate 102 which is composed of, for example, glass or acrylic to construct the large screen display of the thin type. In addition to the ordinary display having an oblong configuration, it is possible to form screens having a variety of shapes including, for example, those having a rectangular configuration with a longer horizontal length, those having a rectangular configuration with a longer vertical length, and those having a circular configuration, by arbitrarily changing the arrangement of the display devices 10. It is also possible to form a curved surface display by previously curving the optical waveguide plate.
FIG. 39 shows a schematic cross section of the display device 10. The display device 10 comprises an actuator substrate 12, an optical waveguide plate 14, and a plurality of crosspieces 16 allowed to intervene between the both. The optical waveguide plate 14 and the crosspieces 16 are joined to one another by the aid of an adhesive 17. The actuator substrate 12 has an actuator element 18 which is displaceable toward the actuator substrate 12 or toward the optical waveguide plate 14 at a position surrounded by the plurality of crosspieces 16. A unit dot 22 is constructed by the actuator element 18 and a picture element assembly 20 which is provided on the actuator element 18. As described later on, the display device 10 is provided with a plurality of unit dots 22.
The unit dot 22 is specifically constructed as follows. That is, a hollow space 24 is formed at the inside of the actuator substrate 12 corresponding to the position at which the actuator element 18 is provided. Therefore, the portion of the actuator substrate 12, at which the actuator element 18 is provided, has a thin wall thickness as compared with the other portions (the portion will be hereinafter referred to as xe2x80x9cthin-walled sectionxe2x80x9d 12a).
The actuator element 18 comprises a shape-retaining layer 26 which is composed of a piezoelectric/electrostrictive material or an anti-ferroelectric material, a column electrode 28 which is provided on the lower surface of the shape-retaining layer 26, and a row electrode 30 which is formed over a range from the side surface to the upper surface of the shape-retaining layer 26 with a through-hole 13 provided through the actuator substrate 12 from the lower surface of the actuator substrate 12.
The picture element assembly 20, which is formed on the actuator element 18, is a laminate comprising a white scattering element layer 32, a color filter layer 34, and a transparent layer 36. As described later on, when the picture element assembly 20 abuts against the optical waveguide plate 14, the light 38, which is guided through the inside of the optical waveguide plate 14, is reflected. In this process, the light 38 is colored to have a color corresponding to a color of the color filter layer 34, and the light 38 is emitted to the outside of the optical waveguide plate 14. Accordingly, the unit dot 22 emits light with the color corresponding to the color filter layer 34.
Therefore, when the color of the color filter layer 34 is varied for each of the unit dots 22 so that the light emission is obtained with the red color for a certain unit dot 22, the green color for another unit dot 22, and the blue color for still another unit dot 22, then the entire display device 10 is provided with the three primary colors of light. Therefore, the display device 10 is capable of emitting all colors. In the following description, a group, in which one or more unit dots 22 for causing red light emission, is referred to as xe2x80x9cred dotxe2x80x9d, and it is designated by reference numeral 22R. Similarly, groups, in which one or more unit dots for causing green light emission and blue light emission, are referred to as xe2x80x9cgreen dotxe2x80x9d (designated by reference numeral 22G) and xe2x80x9cblue dotxe2x80x9d (designated by reference numeral 22B) respectively.
In general, as shown in FIG. 40, the red dot 22R, the green dot 22G, and the blue dot 22B are arranged in an aligned manner. A picture element (pixel) 40 is constructed by them. The display device 10 comprises a plurality of such picture elements 40, and it displays a variety of colors depending on the light emission states of the red dot 22R, the green dot 22G, and the blue dot 22B. As a result, an image is displayed on the large optical waveguide plate 102 of the large screen display 100.
In the display device 10 constructed as described above, as shown in FIG. 39, when the upper end surface of the picture element assembly 20 (transparent layer 36) abuts against the optical waveguide plate 14, then the light 38, which is guided through the inside of the optical waveguide plate 14, is transmitted through the transparent layer 36 and the color filter layer 34, and then it is reflected by the white scattering element layer 32. The light is emitted as the scattered light 42 to the outside of the optical waveguide plate 14. As a result, the display device 10 causes light emission with the color corresponding to the color filter layer 34.
When the voltage is applied between the column electrode 28 and the row electrode 30, for example, if the column electrode 28 is the positive electrode, then the electric field, which is directed from the column electrode 28 to the row electrode 30, is generated. As a result, the polarization is induced in the shape-retaining layer 26, and the strain, which is directed to the column electrode 28, is generated in the shape-retaining layer 26. As shown in FIG. 41, the strain cause bending deformation of the actuator element 18. The entire actuator element 18 is displaced downwardly, and the upper end surface of the picture element assembly 20 is separated from the optical waveguide plate 14. In this situation, the light 38 is not reflected by the picture element assembly 20, and it is guided through the inside of the optical waveguide plate 14. Therefore, the light 38 is not emitted to the outside of the optical waveguide plate 14. That is, in this situation, the display device 10 is in the light off state.
When the applied voltage is changed so that the difference in electric potential between the both electrodes 28, 30 is decreased, the strain of the shape-retaining layer 26 is removed in accordance with a hysteresis manner. That is, the strain of the shape-retaining layer 26 is scarcely removed at the beginning at which the difference in electric potential between the column electrode 28 and the row electrode 30 is initially decreased. When the difference in electric potential is further decreased, the strain is quickly removed. Finally, the upper end surface of the picture element assembly 20 abuts against the optical waveguide plate 14 again, and thus the display device 10 is in the light emission state (see FIG. 39).
As clearly understood from the above, the luminance and the light emission color of the display device 10 can be adjusted by adjusting the difference in electric potential between the column electrode 28 and the row electrode 30. Further, it is possible to switch the display device 10 from the light emission state to the light off state, or from the light off state to the light emission state.
The light emission state or the light off state of the display device 10 is entirely displayed on another surface (principal surface) different from the surface of the large optical waveguide plate 102 on which the display devices 10 are arranged. That is, the principal surface functions as the display screen of the large screen display 100.
The display device 10 is produced, for example, as follows. At first, a plurality of segment plates composed of fully stabilized zirconium oxide or the like are placed on a flat plate composed of fully stabilized zirconium oxide or the like. Further, a thin-walled flat plate composed of fully stabilized zirconium oxide or the like is placed on the segment plates.
The sintering treatment is applied in this state to join these components to one another. Thus, the actuator substrate 12, which has the hollow space 24 and the thin-walled section 12a, is obtained. The through-hole 12b, which extends from the lower surface of the actuator substrate 12 to the hollow space 24, is previously provided before the sintering treatment. Accordingly, it is possible to suppress any deformation of the substrate 12 which would be otherwise caused by the sintering treatment, because of the following reason. That is, even when the gas in the gap to be formed into the hollow space 24 is expanded during the application of the sintering treatment, the amount of the gas corresponding to the expansion is discharged to the outside through the through-hole 12b. 
The through-hole 13 is formed by mutually superimposing through-holes which are previously provided through the flat plate, the segment plate, and the thin-walled flat plate respectively, or by providing the through-hole through the substrate 12 after the sintering treatment.
Subsequently, the column electrode 28, the shape-retaining layer 26, and the row electrode 30 are formed in this order by means of the film formation method including, for example, the photolithography method, the screen printing method, the dipping method, the application method, the electrophoresis method, the ion beam method, the sputtering method, the vacuum vapor deposition method, the ion plating method, the chemical vapor deposition (CVD) method, and the plating. Thus, the actuator element 18 is provided on the actuator substrate 12.
Subsequently, a precursor of the crosspiece 16 is formed so that the actuator element 18 is surrounded thereby. That is, a thermosetting resin is deposited on the actuator substrate 12 so that the actuator element 18 is surrounded thereby. The adhesive 17 is applied to the upper end surface of the precursor of the crosspiece 16.
Subsequently, a precursor of the white scattering element layer 32, a precursor of the color filter layer 34, and a precursor of the transparent layer 36 are formed in this order on the actuator element 18. Accordingly, a precursor of the picture element assembly 20 is obtained. The respective precursors can be also formed by means of the film formation method as described above.
Subsequently, the optical waveguide plate 14 is placed on the upper end surface of the precursor of the crosspiece 16 and the precursor of the picture element assembly 20. The pressure is applied from both of the upper surface of the optical waveguide plate 14 and the lower surface of the substrate 12.
The entire body is subjected to the heat treatment in this state to simultaneously harden the precursor of the crosspiece 16, the adhesive 17, and the picture element assembly 20. In accordance with the hardening, the crosspiece 16 and the picture element assembly 20 are formed. Further, the crosspiece 16 is joined to the optical waveguide plate 14 by the aid of the adhesive 17, and the picture element assembly 20 is joined onto the actuator element 18. Thus, the unit dot 22 (display device 10) is consequently completed.
When the display device 10 is produced as described above, a fear arises such that the upper end surface of the precursor of the picture element assembly 20 adheres to the optical waveguide plate 14 when the optical waveguide plate 14 and the substrate 12 are pressed. If the hardening treatment is performed for the picture element assembly precursor in this state, the picture element assembly 20 is not sufficiently separated from the optical waveguide plate 14 in some cases, even when the display device 10 is allowed to be in the light off state by displacing the actuator element 18 toward the substrate 12.
If such a situation takes place, a part of the light 38, which is guided through the optical waveguide plate 14, is reflected and/or scattered by the picture element assembly 20. That is, a slight amount of light is released to the outside of the display device 10, resulting in such an inconvenience that the light off state of the display device 10 is incomplete.
In order to solve such a problem, the optical waveguide plate 14 may be placed after hardening the precursor of the picture element assembly 20. However, if the display device 10 is produced as described above, the picture element assembly 20 is slightly contracted as compared with the precursor thereof. Therefore, when the display device 10 is allowed to be in the light emission state, the picture element assembly 20 does not make tight contact with the optical waveguide plate 14 in a sufficient manner. For this reason, a desired luminance is not obtained in some cases.
In view of the above, a technique has been also suggested, in which a light-transmissive liquid is allowed to intervene between the picture element assembly 20 and the optical waveguide plate 14 so that the tight contact performance between the both is improved by allowing the light-transmissive liquid to make contact with the both. However, in this case, the tight contact performance is excessively improved. As a result, the operation to separate the picture element assembly 20 from the optical waveguide plate 14 is slow, and the light emission and the light off of the display device 10 do not follow the image signal.
The present invention has been made in order to solve the problem as described above, an object of which is to provide a display device and a method for producing the display device in which the tight contact performance between an optical waveguide plate and a picture element assembly is improved, and the picture element assembly is separated from the optical waveguide plate reliably and quickly.
In order to achieve the object described above, the present inventors have conceived that an adhesion-suppressing agent is applied or added to the picture element assembly 20 to suppress the adhesion between the picture element assembly 20 and the optical waveguide plate 14. The present inventors initially directed the attention to a releasing agent to be used in the casting operation, because of the following reason. That is, the releasing agent facilitates the release of a cast product from a mold by suppressing the adhesion of the cast product to the mold.
Although the releasing agent prevents the cast product (metal) from the adhesion to the mold (metal), the releasing agent not necessarily prevents the adhesion between the glass or the like (optical waveguide plate 14) and the cured resin (picture element assembly 20). Actually, according to the investigation made by the present inventors, no effect to suppress the adhesion was obtained at all by using a fluorine compound resin commercially available as the releasing agent.
Further, the adhesion-suppressing agent to be used must allow the light 38 to come into the picture element assembly 20 at a high efficiency when the display device 10 is allowed to be in the light emission state. If the adhesion-suppressing agent reflects the light 38, the luminance of the display device 10 is decreased. That is, it is impossible to allow the display device 10 to emit light at a desired luminance.
As clearly understood from the above, it is necessary for the adhesion-suppressing agent that the picture element assembly 20 and the optical waveguide plate 14 are prevented from adhesion when the display device 10 is used, and the light 38 is successfully allowed to come into the picture element assembly 20 at a high efficiency.
In view of the above, the present inventors have made diligent investigations repeatedly for the substance which prevents the adhesion between the picture element assembly 20 and the optical waveguide plate 14 and which allows the light to come into the picture element assembly 20 at a high efficiency. Thus, the present invention has been completed.
That is, according to the present invention, there is provided a display device comprising a substrate having an actuator element, an optical waveguide plate, a crosspiece allowed to intervene between the optical waveguide plate and the substrate for surrounding the actuator element, and a picture element assembly joined onto the actuator element; wherein the picture element assembly has an adhesion-suppressing agent at least at a portion opposed to the optical waveguide plate.
Accordingly, it is possible to remarkably suppress the adhesion of the picture element assembly precursor to the optical waveguide plate when the picture element assembly precursor abuts against the optical waveguide plate. Therefore, when the actuator element is displaced, then the picture element assembly is reliably separated from the optical waveguide plate, and the display device is in the light off state.
The adhesion-suppressing agent may be applied to at least the portion of the picture element assembly opposed to the optical waveguide plate, or it may be added to the picture element assembly. In this arrangement, the adhesion-suppressing agent is preferably added in an amount of 0.01 to 50% by weight, and more preferably 0.1 to 10% by weight. When the amount of addition is within the range as described above, then it is possible to prevent the precursor of the picture element assembly from adhesion to the optical waveguide plate, and it is possible to obtain the picture element assembly involving neither cracks nor hollow cavities. It is also preferable that the adhesion-suppressing agent seeps out to at least the portion of the picture element assembly opposed to the optical waveguide plate.
It is possible to use a silicone-based substance for the adhesion-suppressing agent. In this arrangement, those usable as the silicone-based substance include silicone oil and/or silicone grease and a mixture principally containing at least any one of them. It is preferable that the adhesion-suppressing agent has a refractive index of 1.30 to 1.70, because of the following reason. That is, it is possible to allow the light to come from the optical waveguide plate into the picture element assembly at a high efficiency. More preferably, the refractive index is 1.38 to 1.55, because of the following reason. That is, such a refractive index is close to the refractive index of transparent glass or acrylic which can be utilized as the optical waveguide plate inexpensively and conveniently. Therefore, it is possible to allow the light to come from the optical waveguide plate into the picture element assembly at a higher efficiency.
It is also preferable that the adhesion-suppressing agent is applied to at least a portion of the optical waveguide plate opposed to the picture element assembly.
According to another aspect of the present invention, there is provided a method for producing a display device comprising a substrate having an actuator element, an optical waveguide plate, a crosspiece allowed to intervene between the optical waveguide plate and the substrate for surrounding the actuator element, and a picture element assembly joined onto the actuator element; the method comprising a step of preparing a precursor by adding an adhesion-suppressing agent and other additives to a constitutive material for the picture element assembly; a step of patterning the precursor; and a step of allowing the adhesion-suppressing agent to seep out to at least a portion of the picture element assembly opposed to the optical waveguide plate by aging the precursor.
In this process, it is also preferable that the step of allowing the adhesion-suppressing agent to seep out is performed by applying vibration.
According to still another aspect of the present invention, there is provided a method for producing a display device comprising a substrate having an actuator element, an optical waveguide plate, a crosspiece allowed to intervene between the optical waveguide plate and the substrate for surrounding the actuator element, and a picture element assembly joined onto the actuator element;
the method comprising a step of washing an adhesion-suppressing agent seeped out from the picture element assembly and/or a step of applying the adhesion-suppressing agent to at least a portion of the picture element assembly opposed to the optical waveguide plate.
In this process, the step of applying the adhesion-suppressing agent may be performed such that the adhesion-suppressing agent is applied to at least the portion of the picture element assembly opposed to the optical waveguide plate after washing the adhesion-suppressing agent seeped out from the picture element assembly, or simultaneously with the washing.
It is preferable that the washing step is performed by washing the adhesion-suppressing agent with a highly volatile liquid. It is also preferable that the step of applying the adhesion-suppressing agent is performed by injecting a mixture liquid obtained by mixing or dissolving the adhesion-suppressing agent in a solvent such as a highly volatile liquid.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.